Towards direct nonlinear compression of long-pulse lasers to the femtosecond regime

A concept to efficiently transfer energetic near-nanosecond pulses to the sub-picosecond scale is proposed: Pre-shaped pulses are sent into multi-mirror multi-pass cells which enable km-scale nonlinear propagation. In this way, the initial pulse bandwidth can be extended by more than three orders of magnitude. To verify the concept, spectral broadening of 100-mJ, 300-ps pulses to a sub-300 fs transform-limit in a 1-m diameter multi-pass cell was simulated. Moreover, an 11-mirror cell was set-up and 300 MW peak power pulses were spectrally broadened in air over 297 passes. The experiments showed that excellent beam quality and high-power transmission can be obtained in the investigated multi-mirror arrangements. The concept presents a new gateway for industrial mature, high-power lasers to the ultrafast regime and is, for instance, attractive for high repetition rate laser-particle acceleration applications.